A technique for applying to a power source apparatus a piezoelectric element having a piezoelectric effect capable of converting mechanical energy into electric energy has been heretofore proposed. There have been known various inorganic and organic piezoelectric materials having the piezoelectric effect. Of these piezoelectric materials, a piezoelectric element formed of ceramic such as PZT piezoelectric material has attracted attention in the field and put to practical use.
However, since the conventional piezoelectric element is disadvantageously low in production of electricity, electrical energy generated by the piezoelectric lacks in practicality for a power generating system. Thus, the conventional piezoelectric element could be used for low-power consumption equipment.
To resolve such a problem of the conventional piezoelectric element, the inventor of the present invention has devised a “power generating device” as a power source apparatus using a piezoelectric element, as described in Japanese Utility Model Registration No. 3074105. The devised power generating device charges electric power generated by the piezoelectric element to a desired setting level and discharge the charged electric power in an instant when it reaches the setting level. The electric power energy discharged instantly can be applied for a great range of applications having need of relatively high electricity. In particular, the devised power generating device comprises a capacitor as a charging element, switching means for changing over the operating state to discharge, and a Zener diode serving as a trigger circuit connected to the switching means and capacitor. When the electricity charged in the capacitor exceeds the prescribed constant voltage of the Zener diode, the switching means is operated to discharge.
However, the devised power generating device has the Zener diode used as the trigger circuit determining the quantity of the electricity charged in the capacitor. Because the charged electricity in the capacitor is determined according to the voltage of direct current flowing into the capacitor, the direct current should be monitored constantly. Therefore, it is necessary to operate the trigger circuit all the time, consequently to use too much electricity to operate. The electrical power consumption therefor is unignorable compared with the electric energy generated by the piezoelectric element. The consumption of the unignorable quantity of electricity for monitoring the current with the Zener diode makes it impossible to charge a lot of electricity in the device. Thus, there has been room for further improvement in the devised power generating device used for electric power equipment having need of relatively high electricity.
In the light of the foregoing controversial points of the conventional power source apparatuses, the present invention has the following aims:
An object of the present invention is to provide a power source apparatus using a piezoelectric element, which is capable of supplying sufficient electricity to an external device having need of relatively high electricity.
Another object of the present invention is to provide a power source apparatus capable of charging more electricity without wasting energy for monitoring or determining charged electricity.
Still another object of the present invention is to provide a power source apparatus capable of generating a pseudo-alternating current for determining charged electricity.